1. Field of the Invention
The invention relates to an image forming apparatus using an electrophotographic process or an electrostatic recording process, and particularly to an image forming apparatus such as a copying machine, a printer or a facsimile apparatus.
2. Description of Related Art
Generally in multi-color image forming, use is made of the technique of developing an electrostatic latent image formed by external information with developers of plural colors, successively forming developer images toner images of the plural colors on a photosensitive member which is an image bearing member, and successively or collectively superimposing these toner images of the plural colors on a transferring medium such as paper.
In such a multi-color image forming apparatus, there is, for example, a rotary type developing apparatus having developing apparatuses for plural colors, e.g. black, yellow, magenta and cyan mounted in a rotary member (rotary type developing body) along the rotational circumference thereof, and a so-called rotary developing process of rotating the rotary type developing body to thereby successively move necessary developing apparatuses to a developing position opposed to the photosensitive member which is an image bearing member and perform a developing operation has heretofore been proposed and put into practical use.
On the other hand, in conventional electrophotographic type image forming apparatuses, and above all, particularly multi-color image forming apparatuses for effecting color image forming, utilization is widely made of a two-component developing process of mixing a nonmagnetic toner and a magnetic carrier together and using the mixture as a developer. The two-component developing process, as compared with presently proposed other developing processes, has such merits as the stability of the quality of image and the durability of the apparatus, while on the other hand, the deterioration of the developer, particularly the deterioration of the carrier, due to long-period use has been unavoidable and therefore, the work of interchanging the developer along with the long-period use of the multi-color image forming apparatus has become necessary, and this has led to an increase in a service cost and a running cost.
When this two-component developer is applied to a rotary developing apparatus, there have heretofore been proposed several methods of solving such a problem. There is, for example, a method of loading an interchangeable developer supply cartridge into the rotary type developing body of a developing apparatus to thereby effect the supply of a developer including a toner and a carrier and the collection of the developer (for example, Japanese Patent Application Laid-Open No. 6-308829).
Also, in the rotary developing process, there has been put into practical use a developer discharging process utilizing a change in the acting direction of gravity resulting from the rotational movement of the rotary type developing body to supply the two-component developer to the developing apparatus and discharge the two-component developer from the developing apparatus.
For example, in Japanese Patent Application Laid-Open No. 9-218575, as shown in FIG. 10 of the accompanying drawings, there is disclosed a rotary type developing apparatus 101 having four developing apparatuses 200 uniformly provided in a rotary type developing body 101′ along the circumferential direction thereof. Each of the four developing apparatuses 200 is provided with a developer cartridge 6 containing therein a developer to be supplied. At a developing position P1 opposed to a drum-shaped photosensitive member (photosensitive drum) 113 as an image bearing member, a developer including a toner corresponding to an amount of toner consumed by a developing operation is supplied to the developing apparatus 200, and any excess developer in the developing apparatus 200 is designed to be discharged into the developer cartridge 6 by the utilization of a change in the acting direction of gravity by the rotation of the rotary type developing body 101′. That is, the rotational movement peculiar to the rotary type developing body 101′ is utilized to effect the supply and collection of the developer and therefore, structure is simple, and any reduction in the charging capability of the carrier is prevented without causing the bulkiness of the multi-color image forming apparatus and a rise in the cost thereof.
On the other hand, in Japanese Patent Application Laid-Open No. 10-142888, as shown in FIG. 11 of the accompanying drawings, four developing apparatuses 200 are likewise provided in a rotary type developing body 101′, and design is made such that at a developing position P1 whereat a developing apparatus 200 is opposed to a photosensitive drum 113, a developer discharged from the developing apparatus 200 is temporarily stored in a storing portion 70 protrudedly provided on an end portion of the developing apparatus 200, and a change in the acting direction of gravity by the rotation of the rotary type developing body 101′ is utilized to carry the developer to a cylinder shaft D0 at the center of the rotary type developing body 101′, and the developer is finally collected in a developer collecting container (not shown) provided on an end of the cylinder shaft D0 by a developer transporting member D1 in the cylinder shaft D0. That is, as in the above-described multi-color image forming apparatus, the movement peculiar to the rotary type developing body 101′ is utilized to effect the discharge of the developer and therefore, any reduction in the charging capability of the carrier is prevented without causing the bulkiness of the multi-color image forming apparatus and in addition, design is made such that even when single-color image forming is continued, any excess developer in the developing apparatus at the developing position is discharged to the storing portion outside the developing apparatus 200 without the developing operation being stopped and therefore, the amount of developer in the developing apparatus 200 is maintained within an allowable value without image productivity being reduced.
As described above, in these developing apparatuses wherein the excess developers are discharged, there is adopted a construction in which when the level of the developer in a developing container has become high by a predetermined amount, the developer is scooped out by the utilization of the rotational movement of the rotary type developing body, or a construction in which the excess developer is once collected into the storing portion, and then is collected to a location by the utilization of the rotational movement of the rotary type developing body.
In the developing apparatuses of the above-described publications as shown in FIGS. 10 and 11, however, there has been the possibility of the developers in developing devices flowing out by mistake with the rotation of the rotary type developing body.
Or in order to prevent such unnecessary outflow of the developers, a shutter has been provided on an opening for discharging therethrough the excess developers from the developing apparatus, and driving means (such as a motor) for effecting the opening and closing of this shutter has been controlled so as to completely close the opening except when the excess developers are discharged. Such a shutter mechanism has become complicated in construction and has been a cause of the bulkiness and increased costs of the image forming apparatus.